The present invention is directed to valves and, more particularly, to resilient valve seals used in valves having moveable valve elements.
Valves having resilient valve seals are widely used in commerce and have a multitude of applications. Such valves are commonly used in fluid piping to start and stop the flow of fluid through the piping by opening and closing the valve. The specific construction of such valves differs widely depending on the application in which they are used. Generally, however, a valve of the type involved in the present invention includes a valve housing with an inlet port, an outlet port and a hollow interior defining a flow path between the inlet and outlet ports. A rotatable valve element is mounted within the interior of the valve housing for movement between an open position wherein the valve element permits fluid flow through the valve housing and a closed position wherein the valve element blocks the flow of fluid through the valve housing.
For example, in a butterfly valve, a rotatable disk is pivotally disposed within the hollow interior of the valve housing and is rotatable about an axis generally perpendicular to the flow path between a fully open position, in which it is generally parallel to the flow path, and a fully closed position in which it is generally perpendicular to the flow path. In the case of a spherical plug valve (also sometimes referred to as a "ball valve"), a rotatable plug or "ball" is pivotally disposed within the hollow interior of the valve housing and is rotatable between open and closed positions. In either case, the rotatable valve element is mounted to a shaft, which is itself rotatably mounted to the valve housing. As is well known in the art, the shaft may be connected to a mechanical drive mechanism or operated manually to rotate the shaft and thereby rotate the valve element within the valve body between the open and closed positions.
The interior surface of the valve body, which defines the flow path, includes an internal annular groove adapted to receive and retain a valve seal. The internal annular groove is located so that at least a portion of the valve seal retained therein lies in the plane of the valve element, perpendicular to the flow path and located so that it will engage with the valve element in a leak-tight engagement when the valve element is rotated to its closed position. The valve seal may be retained in the annular groove in a variety of ways well known in the art, including adhesives, frictional engagement, welding, and riveting.
In some prior art valve structures, such as the one disclosed in U.S. Pat. No. 3,544,066 (the '066 patent), a curable polymeric material, such as an epoxy resin, is used to retain the valve seal within the internal annular groove of the valve body. First, the valve seal is inserted into the internal annular groove. Then, the epoxy resin or other polymeric material is introduced, in liquid form, between the annular exterior surface of the seal and the internal annular groove. Finally, the resin is allowed to cure to a solid condition. The annular exterior surface of the valve seal disclosed in the '066 patent includes a plurality of annular ridges, which grippingly engage the cured resin and help to retain the seal within the groove.
In general, under low stress conditions (e.g., under low differential pressure conditions), as in normal opening and closing of the valve where any throttling action is brief, cumulative circumferential movement of the valve seal will usually not result in any significant increase in the seal's cross-section. However, under higher stress conditions, seals of the type disclosed in the '066 patent may fail to maintain an effective seal. For example, under extended periods of throttled flow, where an extreme pressure differential exists between the upstream and downstream sides of the valve (e.g., when a valve is only slightly open and fluid is forced through a highly restricted area), pressures acting on the seal may cause portions of the seal to slip circumferentially along the internal annular groove of the valve housing. Such circumferential slippage causes thickening or "bulging" of the seal (i.e., an increased cross-sectional area of the seal) in the areas of throttled flow, and stretching or "thinning" of the seal (i.e., a decreased cross-sectional area of the seal) in other areas. In cases of extreme circumferential slippage, thickened or "bulged" sections of the seal may interfere with proper closing of the valve, may result in shear damage to the seal, and may overstress actuator components. In addition, in the areas of the seal where stretching or "thinning" occurs, higher upstream pressures may be introduced behind the seal through the reduced cross-sectional area of the seal in tension, which can result in those portions of the seal being pulled out of the internal annular groove (referred to as a "blowout").
Thus there is a need for a valve seal that will withstand high stress flow conditions without losing its ability to maintain an effective seal. Further, in certain extremely high stress conditions, such as a throttled flow condition, there is a need for a valve seal that will resist circumferential slippage of portions of the valve seal. Still further, there is a need for a valve seal having all of the above-described advantages over the prior art and which does not require a complex or cumbersome installation.